On 5/31/19, Nathan Sidwell <nat...@acm.org> wrote:
> On 5/30/19 5:38 PM, Segher Boessenkool wrote:
>> On Thu, May 30, 2019 at 07:08:45PM +0200, Martin Jambor wrote:
>>> Interesting, I was also puzzled for a moment. But notice that:
>>>
>>> int main ()
>>> {
>>> _Float128 x = 18446744073709551617.5f128;
>>> _Float128 y = __builtin_roundf128 (x);
>>> }
>>>
>>> behaves as expected... the difference is of course the suffix pegged to
>>> the literal constant (see
>>> https://gcc.gnu.org/onlinedocs/gcc-9.1.0/gcc/Floating-Types.html).
>>>
>>> I would also expect GCC to use a larger type if a constant does not fit
>>> into a double, but apparently that does not happen. I would have to
>>> check but it is probably the right behavior according to the standard.
>>
>> 6.4.4.2/4: "An unsuffixed floating constant has type double." I don't
>> think your suggestion would be okay?
>
> Not only that, but
>
> 1) there isn't a literal suffix to mean 'double', so one couldn't
> override that extended type.
There's not a standard one, but there is 'D' or 'd' as a GNU
extension. The fact that it's nonstandard, though, is what causes some
projects to ignore -Wunsuffixed-float-constants:
https://lists.gnu.org/archive/html/bug-gzip/2011-11/msg00017.html
> 2) how do you define 'doesn't fit'? decimal 0.1 has a recurring binary
> representation. Should that become the longest floating point type?
>
> nathan
>
> --
> Nathan Sidwell
>
